DESCRIPTION (Verbatim from the Applicant's Abstract): There is a critical need for fundamentally new classes of low molecular weight magnetic resonance (MR) contrast agents with greater molar relaxivity. It is postulated that molecular hexagadolinium cluster compounds will possess multiplied molar relaxivity over that of current monogadolinium chelates. Molecular geometry considerations suggest a new and efficient relaxation mechanism based on hydrogen bonding of water molecules to bridging oxo and hydroxo groups in the above complexes. This hypothesis will be tested by synthesizing a number of chelated hexagadolinium cluster compounds and measuring their relaxivities. The new compounds will be characterized structurally and spectroscopically and their relaxivities measured in vitro in aqueous media of varying viscosity on a relaxometer, a clinical MR scanner, and several high field NMR spectrometers. This proposal brings together expertise in contemporary inorganic and cluster chemistries, diagnostic radiology and experimental NRI to investigate new strategies in contrast agent design. This combined expertise provides a mechanism for rational design of a new class of contrast agents with the goal of improving early detection, staging, therapeutic planning and surveillance of cancer.